Function run_cast 

pub fn run_cast<R, F>(
    input: R,
    frame: Frame,
    sink: F,
) -> Result<usize, AppError>
where
    R: BufRead,
    F: FnMut(&InjectionCommand) -> Result<(), AppError>,

Drive a cast: read from input, translate per frame, and hand each InjectionCommand to sink (which delivers + flushes it). Returns the number of commands emitted.

Processing is incremental (line-by-line or byte-by-byte) so a streaming producer is forwarded in real time rather than buffered to EOF.

Errors

AppError on a stdin read error, a malformed ndjson line, or a sink error (delivery failure).